In accordance with the recent expansion of optical communication networks, not only sufficient reliability but also a further reduction in size and weight, higher density, and an improvement in workability have been required of optical cables.
As an optical cable realizing a reduction in size and weight, higher density, and improved workability, one with so-called rollable optical fiber ribbons, for instance, has been known, in which only two adjacent fibers out of three single-core coated optical fibers or more arranged in parallel are bonded by each resin part, the resin parts are longer in length than non-resin parts, and the resin parts adjacent in a width direction are spaced apart from each (see, for example, References 1 and 2).
Being small in bending anisotropy, such an rollable optical fiber ribbon can be cylindrically rolled or folded when housed in a cable, which enables a reduction in size and weight and higher density of the cable. In addition, the optical fibers each may be easily branched from the optical fiber ribbon and when connected, the optical fibers can be disposed in a predetermined arrangement, which enables the fibers to be collectively connected at one time.
However, in an optical cable in which these conventional rollable optical fiber ribbons are densely packed, a large strain is applied to the single-core coated optical fibers when the optical cable is bent. Accordingly, it is not possible to ensure sufficient long-term reliability. Further, this optical cable is not always satisfactory in terms of connection workability of the optical fiber ribbons. Regarding such problems, the patent reference 1 discloses one in which, in order to reduce a strain when the optical cable is bent, the resin parts each have such a thickness and a length as to easily buckle when an external force is applied in the width direction of the optical fiber ribbons. However, its effect is limited and is not fully satisfactory.